North Sea wind farms may be reshaping sediment flows by 1.5 million tons a year - Earth - Earth Sciences - Environment

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Offshore wind farms are an important pillar of the European Union's strategy for renewable energy—by 2050, the EU aims to increase capacity in the North Sea more than tenfold. A new study by the Helmholtz-Zentrum Hereon shows that the expansion of wind farms can alter the natural transport and deposition of sediments on a large scale and over the long term. The German Bight is particularly affected. The researchers have published their findings in the journal Nature Communications Earth & Environment.

Redistribution of sediment and carbon

Suspended particles are constantly being moved around the North Sea, originating from the stirring-up of local seabed sediments by waves and currents, as well as from material carried in from the Atlantic Ocean through the English Channel, or from rivers. This material travels through repeated cycles of settling and resuspension until it finally accumulates as mud in calmer areas where currents are weak.

Offshore wind turbines are barriers in the air and in the water. They influence the stratification of the sea into warmer and colder water layers and slow down currents over a wide area throughout the North Sea. These factors determine how mud and organic particles are transported through the ocean and where they deposit. Hereon researchers have now discovered that existing wind farms in the North Sea are already causing a significant spatial redistribution of these sediments. This affects up to 1.5 million tons of mud annually—and the carbon bound within it.

Sediments consist in part of the remains of dead marine animals and plants. This organic material contains particulate organic carbon (POC), which sinks to the seafloor with the particles and can be stored there for centuries. The seafloor is therefore referred to as a carbon sink. Oceans thus make an important contribution to global carbon sequestration and help mitigate climate change.

German Bight is particularly affected

The researchers used a new computer model that, for the first time, combines calculations of the atmosphere, waves, currents, and sediment transport in the North Sea. The data is based on previous Hereon studies on the impact of offshore wind turbines on air and ocean currents.

"Our simulations suggest that these amounts will accumulate increasingly over the coming decades as offshore wind farms expand. This could affect the long-term functioning of the ecosystem and carbon storage in the North Sea," says the study's lead author, Jiayue Chen, from the Hereon Institute of Coastal Systems—Analysis and Modeling. Notably, about 52% of the total sediment redistribution occurs in the German Bight. "This highlights this region as particularly affected."

As a next step, the researchers plan to investigate how these changes specifically affect particularly sensitive coastal areas like the Wadden Sea, which relies on a continuous supply of sediment to compensate for rising sea levels. They are also examining how these effects influence the role of the ocean as a carbon sink.

"With an improved understanding of sediment distribution and carbon storage in the North Sea, we can assess long-term risks to coastal stability, navigational safety in shipping, and the functioning of ecosystems in the German Bight," says Chen. "Our findings provide a valuable foundation for the sustainable expansion of offshore wind energy and help decision-makers in politics, business, and industry to plan new wind farms in an environmentally friendly way." 

Provided by Helmholtz Association of German Research Centres  

by Torsten Fischer, Helmholtz Association of German Research Centres

edited by Lisa Lock, reviewed by Robert Egan 

Source: North Sea wind farms may be reshaping sediment flows by 1.5 million tons a year